Unit 3Optics and light

lesson 1:reflaction revision

Define visible light :It is a form of energy that we can detected by our eyes

Light speed is:3×108 m/s

law of reflection

• When light is reflected the incidence ray, the reflected ray, and normal all lie in the same plane

• Angle of reflection =angle of incidence

Read pg 126 in physics for you

Reflection from a mirror:

Incident ray

Normal

Reflected ray

Angle of incidence Angle of reflection

Mirror

Using mirrors

Two examples:

1) A periscope

2) A car headlight

Application of reflection any of a number of optical instruments that enable the user to view objects that are not in the direct line of vision, such as one in a submarine for looking above the surface of the water. They have a system of mirrors or prisms to reflect the light and often contain focusing lenses

يستخدم الغواصة فى البيريسكوبفكرة لكن و المرآتين من بدال منشورين  .  يكون الحالتين ففى واحدة العملو متقابلين العاكسان السطحانينحرف بحيث وضعهما يكون و متوازيينزاوية السطح على الساقط الضوء مسار

درجة 90مقدارها

Refraction

Camera consists of lenses of glass or convex and depends in its work on the refraction

of light

AIR

Critical angle (2)• When we increase the angle of incidence (i),

the angle of refraction (r) increases until ......

AIR

glassglass

AIR

glass

AIR

glass

i

r

normal

AIR

glass

Critical angle (3)• when the angle of refraction is 90o, the incident angle is called the critical angle (C).

AIR

glass

r90o

normal

iC

Total internal reflection

• When the incident angle is larger than the critical angle, total internal reflection will occur (at the interface).

water

AIR

Next

Application of total internal reflection

mirage

rainbow

optical fibersPg:131

• A mirage is a naturally occurring optical phenomenon in which light rays are bent to produce a displaced image of distant objects or the sky.

الصحراوي • السراب

الصحراوي؟ السراب يحدث كيف

االرض سطح حرارة درجة ترتفع ساطعة الشمس تكون عندماالهواء حرارة درجة فتكون فوقها التي الهواء طبقة فتسخن

االشعة تنتقل وهكذا سخونة أقل تليها التي الطبقة فيبارد هواء منطقة من االرض سطح على االجسام عن الصادرة

الفاصل السطح عند االشعة فتنكسر أسخن أخرى الى نسبيامن الفاصل السطح على المقام العمود عن مبتعدة بينهماالسقوط زاوية تصل أن الى كذلك وتستمر السقوط نقطة

كلي انعكاس فتنعكس الحرجة الزاوية من أكبر زاوية الىالمسار عبر الناظر عين الى الضوء يسير لذلك ونتيجة داخلى

مقلوب خيال أنه على المجاور الشكل في المبين

Optical fibres

Optical fibres the angle at which the ray meets the normal at the surface is always much more than the critical angle, so the ray continues down the fiber , with total internal reflection. at the other hand , we can see the light after many total internal reflection .

Optical fibers in communicationfiber-optic cables are now widely used in communication for carrying telephone and tv signals. if there are any scratches on the fiber, the light can escape, because a ray can meet the surface of the scratch with an angle of incidence less than the critical angle. This is easily cured by coating the fiber with a tougher outside layer, made of plastic or glass with a lower absolute refractive index.

• Why is the sky blue?• A clear cloudless day-time sky is blue

because molecules in the air scatter blue light from the sun more than they scatter red light. When we look towards the sun at sunset, we see red and orange colours because the blue light has been scattered out and away from the line of sight.

Sunsets

• When the air is clear the sunset will appear yellow, because the light from the sun has passed a long distance through air and some of the blue light has been scattered away. If the air is polluted with small particles, natural or otherwise, the sunset will be more red. Sunsets over the sea may also be orange, due to salt particles in the air, which are effective Tyndall scatterers. The sky around the sun is seen reddened, as well as the light coming directly from the sun. This is because all light is scattered relatively well through small angles--but blue light is then more likely to be scattered twice or more over the greater distances, leaving the yellow, red and orange colours.

Mirrors and lenses

• A mirror is a reflective surface. Light passes through the glass and hits the silver backing, reflecting off of it. (The angle of incidence equals the angle of reflection.) A lens, on the other hand, does not reflect light; it refracts it. After entering the glass, light refracts differently depending on the shape of the lens and also creates a focal point where the refracting light comes to a point. This differs for different lenses -- convex or concave -- which is why there are different lenses for different types of eyeglasses.

Mirrors and lenses

How we can see

• light from the object will focus on your retinas very precisely. When seeing an object close-up, the focus is blurred very momentarily, but this is unnoticeable, because your eye has an automatic refocusing ability that makes the target clear. This refocusing ability is called "Accommodation," and it works by making the natural lens of the eye larger or more convex in shape. As we get older, we lose more and more of this ability, which is why things close-up start to blur after about 45 years of age.

Our eyes

Sight Conditions

• SHORT-SIGHTEDNESSShort-sighted, also known as near-sight or Myopia, means that the light focuses in front of your retinas or 'too short.' This makes it difficult to see objects in the distance whereas objects close-up are clearer. This occurs when light from the objects seen focus in front of the retina rather than on it. This is believed to happen when the eyeball is slightly too long, and is also known as Axial Myopia.

LONG-SIGHTEDNESS

Long-sighted, also known as far-sight or Hyperopia, means the eyes focus "behind" or 'too long,' which makes it difficult to see objects close up rather than from a distance. This occurs when light from objects viewed will theoretically focus behind the retina rather than on it. However, because the eye is able to naturally fatten the lens and cause light to bend more, this error in focus is overcome. This explains why distance vision is usually good. When the same individual tries to look at something up close, much more effort is required, as light from a near object will fall much further back behind the retina. Near vision is therefore worse.

Apparent Depth Real Depth of waterWe see the objects under water closer than their real depth to the surface.

• ؟ الحقيقي عمقها من أقل عمق على حوض في السمكة تبدو لماذا

العمود عن مبتعدة سطح عند تنكسر الضوئية االشعة أن هو الجواببالنسبة السمكة خيال يشكل المنكسرة االشعة هذه وامتداد المقام

. االرض سطح على للمشاهد

الخيال ) (: موضع عنده الجسم أن للمشاهد يبدو الذي البعد على يطلق. الظاهري البعد

مادته ) انكسار معامل خفيف وسط من الضوئي الشعاع انتقال عند ) البعد( ) يكون كبير مادته انكسار معامل كثيف وسط الى صغير

الحقيقي . البعد من أكبر الظاهري

( مادته انكسار معامل كثيف وسط من الضوئي الشعاع انتقال عند ) البعد( ) يكون صغير مادته انكسار معامل خفيف وسط الى كبير

الحقيقي البعد من أقل . الظاهري

كل هذا عزيزاتيمن مطلوب ماهو

الثالثة الوحدةللفصل الضوء

الثاني الدراسي